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Humidifier help for large house with geothermal in Northern Indiana

I have a fairly large house with 3,300 sq feet on the main floor and a full basement below. The basement is basically completely open. I have a Comfort-Aire HRV070A1C00JRT geothermal unit. My insulation, including the attic, is Iconene open cell spray foam. The house is tight, but I have never done a blower door test. My AC is oversized as is my heat. (I'm going to have to live with it until a replacement becomes necessary). I generally run the fan full time for circulation, however the heat is only required for short periods of time. I also have an HRV. Occupants are myself and my wife with three little girls under 10 years old. My humidity today is 25%. Outside here, near Lafayette, Indiana it is 39 degrees with humidity of 73%. I realize I have a large house (10' ceilings in the basement, 9' upstairs 55,000 cu ft? or so), however it seems really hard to pin down what humidifier to purchase. We have high iron/lime in our water, however it ok after the water softener. I am in a rural area on a well. I am considering the Aprilaire 800 (steam) and the Honeywell TruSteam HM512VPIAQ, along with the Aprilaire 400 hooked to my hot water or the GeneralAire 1137. I know the Honeywell TruSteam is not rated at as high capacity as the Aprilaire 800, but, even though I have a big house, do I really need that large capacity as compared to a house which is not as airtight? I have an oversized geothermal AC primarily because my HVAC installer convinced me the foam wouldn't make such a big difference and simply sized it incorrectly. I point that out because my heat is also oversized and does not run as much as a "normal" unit. I could certain benefit from anyone who has tackled this problem or something similar before. Thank you so much!

I like any steam humidifier, because you dont need the heat on to run it, just the fan, we wire our trusteams to energize the fan on a call for humidification. We have had some problems withthe trusteams, but when they work, they are very effective. Get the 12 gallon a day and you will be fine. I put a 9 gallon in for my uncle and his house is 2800 square feet and is plenty, he also has wood floors.

I have a fairly large house with 3,300 sq feet on the main floor and a full basement below. The basement is basically completely open. I have a Comfort-Aire HRV070A1C00JRT geothermal unit. My insulation, including the attic, is Iconene open cell spray foam. The house is tight, but I have never done a blower door test. My AC is oversized as is my heat. (I'm going to have to live with it until a replacement becomes necessary). I generally run the fan full time for circulation, however the heat is only required for short periods of time. I also have an HRV. Occupants are myself and my wife with three little girls under 10 years old. My humidity today is 25%. Outside here, near Lafayette, Indiana it is 39 degrees with humidity of 73%. I realize I have a large house (10' ceilings in the basement, 9' upstairs 55,000 cu ft? or so), however it seems really hard to pin down what humidifier to purchase. We have high iron/lime in our water, however it ok after the water softener. I am in a rural area on a well. I am considering the Aprilaire 800 (steam) and the Honeywell TruSteam HM512VPIAQ, along with the Aprilaire 400 hooked to my hot water or the GeneralAire 1137. I know the Honeywell TruSteam is not rated at as high capacity as the Aprilaire 800, but, even though I have a big house, do I really need that large capacity as compared to a house which is not as airtight? I have an oversized geothermal AC primarily because my HVAC installer convinced me the foam wouldn't make such a big difference and simply sized it incorrectly. I point that out because my heat is also oversized and does not run as much as a "normal" unit. I could certain benefit from anyone who has tackled this problem or something similar before. Thank you so much!

During winter, maintaining 68^F, 40%RH is a 43^F dew point during the winter. During the rest of the year, you need <50%RH ideally which is 50-55^F dew point. Your outside dew points vary from 0^F to 80^F. 5 occupants add 2 lbs. of moisture per hour typically.
HRV, bathfans, kitchen hood, clothes drier, and wind/stack effect cause all movement air through your home. Ideally, moving 100 cfm of fresh air through your home would be ideal to purge indoor pollutants and renew oxygen year around. Wind and stack effect during cold windy weather can move 100 cfm without any mechanical air movement. Raising the dew point of 100 cfm of infiltrating air from 20^F to the desire 43^F is 1.5 lbs per hour.
Consider, most %RH meters are not accurate at extreme high/low %RH levels.
The over-dryness of your home indicates excess air moving through your home. Minimize the HRV, kitchen hood, bathfan operation, when the outdoor dew points are low and the home is dry.
After minimizing air movement, adding 2 lbs. of moisture per hour should be adequate in your type home. Try a measure amount of moisture per hour in your home estimate the effect. A small internal fan humidifier on the supply duct connected to a cold water line should do. Steam humidifiers use 1 kw per 2-3 lbs. of moisture. This can get pricey. Evaporative humidifiers use 1050 btus per lb. of evaporation. With ground source hp, this is a 60% savings.
Now to the other side of the problem. You need a whole house dehumidifier to maintain <50%RH during the times of the year when the outdoor dew points are +50^F-75^F and you are getting the fresh air change in 4-5 hours you need. Checkout the Ultra-Aire whole house dehus. You will need 2-3 lbs. of dehumdification per hour during high outdoor dew points and low/no cooling loads.
Regards TB

Thanks for the input. What I am doing now to combat the stack effect (really the electric clothes dryer and bathroom fans) is dumping the exaust from my hrv back into my basement. I did borrow two, nine-gallon evaporative humidifiers to test. After basically a day of running, I have brought my house humidity up from 25% to 43%. I was running them both on high settings and will have to turn them down to low. Based on this, I am now thinking about the Aprilaire 700? Do I really need the evaporative units because of my low geothermal air temperatures? I'm thinking the 700 might not be perfect, however it looks like it might be enough.

Thanks for the input. What I am doing now to combat the stack effect (really the electric clothes dryer and bathroom fans) is dumping the exaust from my hrv back into my basement. I did borrow two, nine-gallon evaporative humidifiers to test. After basically a day of running, I have brought my house humidity up from 25% to 43%. I was running them both on high settings and will have to turn them down to low. Based on this, I am now thinking about the Aprilaire 700? Do I really need the evaporative units because of my low geothermal air temperatures? I'm thinking the 700 might not be perfect, however it looks like it might be enough.

Measure the amount of water that the evap humidifiers are putting into the air per day. This will determine the size of the humidifier needed. Can you slow or turn off the HRV during cold weather? Low 24/7 during the other 3 seasons is ok..
Best off with evap humidifier for low maintaince and cost to humidify.
When the outdoor dew points rise +55^F, good ventilation will result in the need for a dehumidifier.
Keep us posted.
Regards TB

a single story home won't have much of any stack effect, especailly with spray foam insulation, while means you attic floor or roof will be sealed up tight if installed right. What you have is negative pressure. IN a tight spray foam home, you shouldn't need additonal humidification, something isnt' right, or it wasn't isntalled correctly and missed a lot of spots or your running the HRV too much.

I have an oversized furnace and so my bypass humidifier runs most of the time on just cool air. I connected it to the hot water. I didn't think the upfront cost as well as maintenance of a truesteam would be worth it. It seems to work fine.

Single story homes DO have stack effect; I know this from experience. It's not as intense as multi-story homes, but it is there, and should be dealt with all the same.

For the OP, sounds to me your HRV operation is excessive in cold weather. Teddy Bear is correct; when outdoor temperatures and dew point temperatures are low, the house may naturally ventilate enough that HRV use is unneeded. An indication of how airtight a house is during cold, dry weather is indoor humidity levels with no HRV in operation and no humidifier running. If it's low, the house could probably use air tightening. Homes that are truly tight trend higher indoor humidity levels on average, and can even require dehumidification if the house is REALLY tight. Fortunately in winter in many locations, the outdoor air is dry enough that dehumidification is nothing more than carefully admitting outdoor air to the structure. But this must be done intelligently, not willy-nilly as is often done.

Electricity makes refrigeration happen.

Refrigeration makes the HVAC psychrometric process happen.

HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.